1. Field of the Invention
The present invention relates to power supply circuits. More specifically, the present invention relates to power supply circuits and associated operating methods for controlling current flow in an AC adapter.
2. Description of the Related Art
Computers such as laptop computers are powered by an AC power source or, if AC power is not available, an installed rechargeable battery. To ensure that a user of a computer has sufficient battery charge available when AC power is only intermittently available and available for a short time, developers and manufacturers of AC adapters, charging circuits and rechargeable batteries have developed battery charging systems and rechargeable batteries that restore charge to the batteries very quickly. The fast charging character of these systems and batteries is achieved by adapting the AC adapter, the charging circuits and the battery to greatly increase the amount of power that is applied to the battery. Present-day AC adapters have increased in power to the range of 65 to 100 watts.
Unfortunately, the large increase in power in charging circuits and AC adapters results in a substantial electrical stress to the power control system. First, a large current surge to the AC adapter occurs when the adapter is connected to AC power lines. Second, a large current surge takes place when the AC adapter is connected to the computer. Peak current surges in excess of 50 amperes have been measured. Peak current surges of this magnitude can be highly destructive to bulk capacitors both in the computer and in the AC adapter. In addition, peripheral system interconnect components are stressed due to inductive coupling of energy between the AC adapter cabling and the interconnect components.